Recent evidence points towards him being related to wikileaks sources. One theory is that he was related to these activities but the government couldn't prove it. Therefore using this to arrest him. There's evidence that supports this theory like the fact that at the time of his arrest the hardware where he stored the info he "stole" weren't confiscated. It's like they didn't care what his charges were.
Link
One of us is no more.
He deserves a eulogy more eloquent than what I am capable of writing. Here's Cory Doctorow's, one of his long time friends.
It's a sad world in which you are being arrested and grand jury'd for downloading scientific journals and papers with the intent to share them.